1. Field of the Invention
The present invention generally relates to sputtering methods and apparatuses, and more particularly to a sputtering method and a sputtering apparatus which are suited for magnetron sputtering and the like.
2. Description of the Related Art
FIG. 1 is a diagram for explaining a conventional sputtering method. In FIG. 1, magnets 2 and 3, which are provided on a magnet base 1, are rotated with respect to a target 8 by a motor (not shown). A peripheral part of the target 8 is held by a target holder 9 within a vacuum chamber of a sputtering apparatus.
During sputtering within the vacuum chamber of the sputtering apparatus, sputtering atoms 11 reach a substrate (not shown) on which a desired film is to be sputtered. In this process of reaching the substrate, a portion of the sputtering atoms 11 become redepositing atoms 12 which are redeposited on the surface of the target 8 due to scattering of a process gas such as Ar gas, to thereby form a redeposited film on the surface of the target 8. On the other hand, a sputtering rate at the surface of the target 8 has a distribution which is mainly dependent upon an intensity of a magnetic field parallel to the surface of the target 8. In FIG. 1, a dotted line indicates the magnetic field, and a one-dot chain line indicates the magnetic field intensity. As a result, a volume of the redeposited film which is formed on the surface of the target 8 is determined by a balance between the sputtering rate and a deposition rate of the redeposited film.
In general, a magnetic circuit used in magnetron sputtering, more particularly, a rotary cathode magnet, is designed to have a weak magnetic field intensity at the peripheral part of the target 8 in order not to subject parts other than the target 8, such as the target holder 9, to the sputtering. For this reason, the deposition rate of the redeposited film becomes high with respect to the sputtering rate at the peripheral part of the target 8, and this causes the deposition of the redeposited film.
FIG. 2 is a diagram showing a relationship between the sputtering rate and the deposition rate of the redeposited film at a location where the intensity of the magnetic field parallel to the target surface (that is, the surface of the target 8) is strong. In addition, FIG. 3 is a diagram showing the relationship between the sputtering rate and the deposition rate of the redeposited film at a location where the intensity of the magnetic field parallel to the target surface is weak. In FIGS. 2 and 3, SQ denotes a sputtering amount (or quantity) of the sputtering atoms 11, and RD denotes a redeposition amount (or quantity) of the redepositing atoms 12. In the case shown in FIG. 3, the redeposition amount RD is large compared to the sputtering amount SQ.
If the deposition amount RD of the redepositing atoms 12 or, the film thickness of the redeposited film becomes greater than or equal to a predetermined value, a delamination of the redeposited film easily occurs due to changes in thermal stress and the like. When the delamination of the redeposited film occurs, a component of the redeposited film may adhere on the substrate to cause a defect or, a cathode may be short-circuited to the ground within the vacuum chamber and cause an operation failure of the sputtering apparatus.
Various kinds of sputtering apparatuses have been proposed, as may be seen from Japanese Laid-Open Patent Applications No. 11-61401, No. 2000-1776, No. 4-63271 and No. 4-63273, for example.
According to the conventional sputtering method, there was a problem in that the deposition amount of the redeposited film becomes large at the peripheral part of the target where the intensity of the magnetic field parallel to the target surface is weak, and the delamination of the redeposited film easily occurs.